Make Cookies: Preheat oven to 350 degrees. Line baking sheets with parchment paper; set aside. Sift flower, coco powder, malt powder, baking soda, and salt together into a medium bowl; set aside.
Put sugar and butter in the bowl of an electric mixer fitted with the paddle attachment; cream until pale and fluffy. Mix in egg and vanilla. Mix in creme fraiche. Mix in 3 tablespoons hot water.On low speed, mix in flour mixture.
Drop dough onto lined cookie sheets with a 1/2 ounce-capacity ice cream scoop, about 3 1/2 inches apart (or use a tablespoon gently shape dough into balls). Bake until tops flatten and cookies are just firm, 10 to 12 minutes. Transfer to wire rack; let cool completely.
make filling: Mix chocolate and butter in a heatproof bowl set over a pan of simmering water, stir occasionally intil smooth. let cool until just warm.
Put malt powder and cream cheese in a clean mixing bowl; return to mixer. Mix on medium until completely smooth. Gradually mix in half and half, then mix in melted chocolate and the vanilla. Refrigerate until thick, about 30 minutes.
Return to bowl to mixer; mix on high speed until fluffy about 3 minutes.
Assemble cookies; spread a heaping tablespoon of filling on one cookie with an offset spatula. Press bottom of second cookie onto filling. Repeat. refrigerate in an air tight container for up to 3 days.